1. Field of the Invention
The present invention relates to a transmission device for differential communication.
2. Description of the Related Art
In a conventional transmission device for differential communication, a power source voltage is applied to a pair of communication lines through a transistor having a small output impedance, a, polarity of the applied voltage is inverted based on a value of transmission data, and thereby the transmission data is transmitted by a differential transmission method.
If a common mode noise having the same phase is superposed to each of the communication lines and potentials of the communication lines increase or decrease, electric current flows in the communication lines so that the potentials are maintained within a range of the power source voltage and a differential output is maintained.
However, the above-described operation cannot deal with a common mode noise that is much larger than the power source voltage. For example, US 2007/0252659 A (corresponding to WO2006/040869) discloses a differential communication system in which a common mode choke coil is provided in series with communication lines and a common mode noise is reduced by the common mode choke coil.
Because the common mode choke coil includes a magnetic substance core and a winding, the common mode choke coil is difficult to be included in an integrated circuit with a transmitting circuit or a receiving circuit. Thus, when a common mode choke coil is used in a differential communication system for restricting a failure due to a common mode noise, there is a difficulty that a substrate area may be increased and a dimension of a transmitting device or a receiving device may be increased and that a cost of a transmitting device or a receiving device may be increased.